1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an ink jet image forming apparatus.
2. Discussion of the Background
Among image forming apparatuses such as printers, facsimile machines, photocopying machines, and multi-function machines thereof, there is an image faulting apparatus employing an ink jet system using a liquid ejection head that ejects droplets of recording liquid (i.e., ink) onto a transfer medium for image formation.
For example, in a printer employing a color ink jet system, images are printed by scanning by a carriage having liquid ejection heads (also referred to as a recording head, print head, or head) or heads having nozzle arrays for black (K), yellow (Y), cyan (C), and magenta (M) ink.
However, when monochrome images are printed in such color printers, the printing surfaces of the other multiple color heads which are not used for the monochrome printing are exposed to the atmosphere, causing clogging due to adhesion of dried ink or impurities to the print heads and thereby preventing the color print heads from ejecting ink properly when color images are printed after the monochrome printing.
Therefore, the color print heads have to be cleaned, which means such things as maintenance ejection of the color ink is required for the other multiple color print heads even when monochrome images are printed. However, this cleaning does consume ink. In addition, electricity is wasted and printing time is unnecessarily increasing. Furthermore, when the cleaning is insufficient, the ink is not properly ejected, resulting in degradation of image quality.
To deal with these problems, for example, Japanese patent application publication no. H02-1327-A describes a system having a first carriage for color print heads and a second carriage for monochrome print heads. The two carriages are combined by a binding mechanism for scanning and printing when printing color images. Only the second carriage scans and prints images when printing monochrome images in order to prevent the print heads on the first carriage from being exposed and drying out.
However, in the approach described in H02-1327-A two separate carriages are detachably attachable to each other, and combined as needed to scan and print images. Therefore, misalignment of the two carriages may occur, leading to degradation of image quality. Despite this problem, however, H02-1327-A does not discuss either the misalignment of the combined carriages or any solution thereto.